Automatic gain control device

Abstract

An automatic gain control device capable of reducing signal saturation or signal distortion caused by out-of-band signals of a filter or delay of a control signal. An AGC response control section compares a level of control voltage (‘V 2 _I terminal’ signal) output from an AGC control section b with a level of control voltage (‘V 3 _I terminal’ signal) output from an AGC control section c. If the ‘V 3 _I terminal’ signal is below the ‘V 2 _I terminal’ signal, an AGC amplifier is controlled by the ‘V 3 _I terminal’ signal. If the ‘V 3 _I terminal’ signal is above the ‘V 2 _I terminal’ signal, the AGC amplifier is controlled by the ‘V 2 _I terminal’ signal. In the latter case, control information of the AGC control section b is replaced by control information of the AGC control section c so that the AGC control section c controls the AGC amplifier c.

1. An automatic gain control device comprising:
 a first variable gain amplifier for amplifying an input signal; 
 a filter for limiting a band of an output signal of the first variable gain amplifier; 
 a second variable gain amplifier for amplifying an output signal of the filter; 
 a third variable gain amplifier for amplifying and externally outputting the output signal of the filter; 
 a first control signal generator for generating a first control signal to control a level of the output signal of the first variable gain amplifier to a predetermined level; 
 a second control signal generator for generating a second control signal to control a level of an output signal of the second variable gain amplifier to a predetermined level and outputting the second control signal to the second variable gain amplifier; 
 a third control signal generator, with a response characteristic that is faster than that of the second control signal generator, for generating a third control signal for controlling a level of an output signal of the third variable gain amplifier to a predetermined level and outputting the third control signal to the third variable gain amplifier; 
 a control signal selector for selecting one of the first and second control signals generated from the first and second control signal generators and outputting the selected control signal to the first variable gain amplifier; and 
 a reference information copier for copying control information of the second control signal generator into the first control signal generator when the control signal output from the second control signal generator is selected as the control signal for the first variable gain amplifier. 
 
   
   
     2. The automatic gain control device as claimed in  claim 1 , further comprising a control information copier for copying control information of the second control signal generator into the third control signal generator, when the control signal output from the second control signal generator is selected as the control signal for the first variable gain amplifier. 
   
   
     3. The automatic gain control device as claimed in  claim 2 , wherein the control information copier copies the control information of the second control signal generator into the third control signal generator when a variation value of the first control signal generated from the first control signal generator per a unit time is less than a predetermined value. 
   
   
     4. The automatic gain control device as claimed in  claim 1 , wherein the control signal selector compares the first control signal output from the first control signal generator with the second control signal output from the second control signal generator, and simultaneously selects one of the first and second control signals, which is capable of lowering a gain of the first variable gain amplifier, to output the selected signal to the first variable gain amplifier. 
   
   
     5. The automatic gain control device as claimed in  claim 1 , further comprising a reference value changer for changing a reference value, which is compared with a level of an input signal, depending on a status of quality information when quality information of a received signal is acquired from a signal demodulation section connected to a rear end of the automatic gain control device,
 wherein the first control signal generator generates the first control signal based on the level of the input signal. 
 
   
   
     6. The automatic gain control device as claimed in  claim 5 , wherein the reference value changer changes the reference value by comparing a level of the first control signal generated from the first control signal generator with a level of the second control signal generated from the second control signal generator, and by comparing a level of a received in-band signal with a predetermined value. 
   
   
     7. The automatic gain control device as claimed in  claim 1 , further comprising a gain distribution adjuster for adjusting a gain distribution in a front end circuit and a rear end circuit of the filter, based on comparison of a level of an out-of-band signal of the filter with a level of an in-band signal of the filter. 
   
   
     8. The automatic gain control device as claimed in  claim 1 , further comprising a signal strength calculator for determining a control voltage V 1  as a strength of an in-band signal of the filter when a control voltage V 3  is at least equal to the control voltage V 1 , and determining a calculated value V, which is expressed by:
     V= V1+( G 3(V1)/ G (V1))(V1−V3), 
 
     as the strength of the in-band signal of the filter when the control voltage V 3  is less than the control voltage V 1 ,
 wherein the control voltage V 3  is the first control signal generated from the first control signal generator, the control voltage V 1  is the second control signal generated from the second control signal generator, G(V 1 ) is an overall gain characteristic with respect to the control voltage V 1 , and G 3 (V 1 ) is a gain characteristic of a front circuit of the filter with respect to the control voltage V 1 . 
 
   
   
     9. An automatic gain control device comprising:
 first variable gain amplifier for amplifying an input signal; 
 a filter for limiting a band of an output signal from the first variable gain amplifier; 
 second variable gain amplifier for amplifying and externally outputting an output signal of the filter; 
 first control signal generator for generating a first control signal to control a level of the output signal of the first variable gain amplifier to a predetermined level; 
 second control signal generator for generating a second control signal to control a level of an output signal of the second variable gain amplifier to a predetermined level and outputting the second control signal to the second variable gain amplifier; 
 control signal selector for selecting one of the first and second control signals output from the first and second control signal generators and outputting the selected control signal to the first variable gain amplifier; and 
 reference information copier for copying control information of the second control signal generator into the first control signal generator, when the control signal output from the second control signal generator is selected as the control signal for the first variable gain amplifier. 
 
   
   
     10. The automatic gain control device as claimed in  claim 9 , wherein the control signal selector compares the first control signal output from the first control signal generator with the second control signal output from the second control signal generator, and simultaneously selects one of the first and second control signals, which is capable of lowering a gain of the first variable gain amplifier, to output the selected signal to the first variable gain amplifier. 
   
   
     11. The automatic gain control device as claimed in  claim 9 , further comprising a reference value changer for changing a reference value, which is compared with a level of an input signal, depending on a status of quality information when quality information of a received signal is acquired from a signal demodulation section connected to a rear end of the automatic gain control device,
 wherein the first control signal generator generates the first control signal based on the level of the input signal. 
 
   
   
     12. The automatic gain control device as claimed in  claim 11 , wherein the reference value changer changes the reference value by comparing a level of the first control signal generated from the first control signal generator with a level of the second control signal generated from the second control signal generator, and by comparing a level of a received in-band signal with a predetermined value. 
   
   
     13. The automatic gain control device as claimed in  claim 9 , further comprising a gain distribution adjuster for adjusting a gain distribution in a front end circuit and a rear end circuit of the filter, based on comparison of a level of an out-of-band signal of the filter with a level of an in-band signal of the filter. 
   
   
     14. The automatic gain control device as claimed in  claim 9 , further comprising a signal strength calculator for determining a control voltage V 1  as a strength of an in-band signal of the filter when a control voltage V 3  is at least equal to the control voltage V 1 , and determining a calculated value V, which is expressed by:
     V= V1+( G 3(V1)/ G (V1))(V1−V3), 
 
     as the strength of the in-band signal of the filter when the control voltage V 3  is less than the control voltage V 1 ,
 wherein the control voltage V 3  is the first control signal generated from the first control signal generator, the control voltage V 1  is the second control signal generated from the second control signal generator, G(V 1 ) is an overall gain characteristic with respect to the control voltage V 1 , and G 3 (V 1 ) is a gain characteristic of a front circuit of the filter with respect to the control voltage V 1 .